Our objective is to promote the immune rejection of tumors by removing serum factors enhancing their growth. Serum factors, e.g. tumor-specific antibody or complexes of tumor antibody with tumor antigen, can enhance the growth of tumors in many animals. We postulate that in these situations, the removal of the "enhancing" factor may retard or prevent tumor growth. This possibility will be tested by selectively removing enhancing serum factors in an animal-tumor system in which such factors are present. The animal-tumor system elected for these studies has been the B16 melanoma in C57BL/6J mice. We have quantitated the normal growth of this tumor and have demonstrated a humoral antibody response to antigens associated with it by a radioisotopic antigen binding assay. We now plan to determine whether serum factors are enhancing the growth of this tumor. If so, an attempt will be made to remove these factors by exchange plasma transfusions using normal mice plasma. This technique has been successfully employed in our laboratory to decrease circulating levels of antibody by 60-70 percent without decreasing the number of sensitized lymphocytes. The effect of this procedure on tumor growth and mortality will be compared to that in control groups in whom exchange transfusions are performed but enhancing factors not removed.